Precisely controlling the quantity and timing of the fuel delivered to a combustion chamber of an internal combustion engine may lead to an increase in engine efficiency and/or a reduction in the generation of undesirable emissions. To improve control over the quantity and timing of fuel delivery, a typical fuel injection system, and in particular, a fuel injector, may include an intensifier assembly that pressurizes the fuel for use in the combustion chamber. Intensifier assemblies may be of the dual-fluid type or the single-fluid type.
In a dual-fluid type intensifier assembly, fuel enters a pressurization chamber of the intensifier assembly and a relatively high pressure actuation fluid, such as engine lubricating oil, enters a control chamber of the intensifier assembly. A controllable valve, usually a solenoid type valve, controls the flow of high pressure actuation fluid to the control chamber by opening and closing a high pressure inlet. Activating the solenoid valve opens the high pressure inlet allowing the high pressure activation fluid to act on one end of the intensifier piston. The other end of the intensifier piston is in contact with the fuel in the pressurization chamber. Because the high pressure activation fluid in the control chamber has a higher pressure than the fuel and because the high pressure activation fluid acts on a surface area of the intensifier piston that is larger than the surface area in contact with the fuel, the high pressure activation fluid drives the intensifier piston towards an advanced position. As the intensifier piston moves towards its advanced position, it acts on the fuel in the pressurization chamber, increasing the fuel pressure. When the pressure caused by the intensifier piston reaches a valve opening pressure, a spring biased needle check opens to commence fuel injection into a combustion chamber of the engine. Deactivating the solenoid valve ends the injection cycle and releases pressure in the control chamber of the intensifier assembly. Releasing the pressure in the control chamber drops the fuel pressure in the pressurization chamber causing the needle check, under the influence of its return spring, to close. Closing the needle check ends fuel injection.
Single-fluid type intensifier assemblies do not utilize high pressure engine oil as the actuation fluid. Rather single-fluid intensifier assemblies utilize the same fluid (fuel) for use in both the pressurization chamber and the control chamber. In a single-fluid intensifier assembly, the engine supplies pressurized fuel to the fuel injector from a high pressure supply, such as a high pressure common rail. The fuel injector selectively supplies the pressurized fuel to the control chamber to act on one end of the intensifier piston. Fuel is also supplied to the pressurization chamber of the intensifier assembly. When the fuel is selectively supplied to the control chamber, it acts on the intensifier piston. The intensifier piston then acts on the fuel in the pressurization chamber increasing the pressure of the fuel in the pressurization chamber above the pressure of the fuel supplied to the control chamber. This occurs because the fuel in the control chamber acts on a larger surface area of the intensifier piston than the fuel in the pressurization chamber.
U.S. Pat. No. 6,453,875 (“the '875 patent”), for example, discloses a single-fluid type intensifier assembly for a fuel injector. The '875 patent discloses a fuel injection system including a pressure step-up unit having a pressure chamber in communication with a nozzle chamber via a pressure line and a pressure storage chamber. Control of the pressure step-up unit is effected hydraulically by imposition of pressure from a differential chamber of the pressure step-up unit. The '875 patent however, requires a bypass line parallel to the step-up unit to provide fuel to the nozzle. The addition of the bypass line utilizes valuable space in such tightly confined systems, and adds to the cost and complexity of the system.
The method and apparatus of the present disclosure solves one or more of the problems set forth above.